Contact fuse

ABSTRACT

The contact fuse of a parachute restrained ordinance device is provided with various means for insuring detonation at ground level. Series connected crush switches externally mounted on the nose of the ordinance device activate the firing circuits when contact is made with soft ground. A cruciform-shaped open guard member both prevents switch contact with the forest canopy and permits actuation by soft ground surface. An internally disposed crush switch placed between a fixed position foam pad member and a face plate mounted on a sheat joint member activates the firing circuits while preventing premature fuse wipe-out when solid ground is contacted. A jettisonable cover cone prevents premature detonation while the ordinance device is being carried by an aircraft.

United States Patent 11 1 Folkins NOV. 6, 1973 1 1 CONTACT FUSE Glenn 0. Folkins, Placitas, N. Mex.

[73] Assignee: The United States of America as represented by the United States Atomic Energy Commision, Washington, DC.

[22] Filed: Dec. 14, 1971 [21] Appl. No.: 207,736

[75] Inventor:

Samburoff 102/73 R X Kupec et a1 102/73 R Primary ExaminerSamuel W. Engle Att0rneyHarry A. Herbert, Jr. et a1.

[5 7] ABSTRACT The contact fuse of a parachute restrained ordinance device is provided with various means for insuring detonation at ground level. Series connected crush switches externally mounted on the nose of the ordinance device activate the firing circuits when contact is made with soft ground. A cruciform-shaped open guard member both prevents switch contact with the forest canopy and permits actuation by soft ground surface. An internally disposed crush switch placed between a fixed position foam pad member and a face plate mounted on a sheat joint member activates the firing circuits while preventing premature fuse wipeout when solid ground is contacted. A jettisonable cover cone prevents premature detonation while the ordinance device is being carried. by an aircraft.

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INVENTOR. GLEN N O- FOLKINS mzw HTTOR vN EYS CONTACT FUSE BACKGROUND OF THE INVENTION This invention relates to contact fuses of the type used in parachute-dropped ordinance devices, and in particular to refinements thereof directed toward preventing premature deterioration by rain, flying debris, forest canopy, and the like.

Conventional fusing systems have been found to be unreliable when used on weapons whose detonation is desired substantially at ground level when such weapons are used in certain nonideal environments. Various conditions have been found to cause premature detonation and failure to detonate at all. Rain and airborne debris have on occasion prematurely detonated the weapon while being carried by an aircraft. After release from the aircraft the weapon can also be prematurely detonated by tree limbs and the like. Failure to detonate can be caused by impacts in the soft mud, loose sand, silt, and the like, or by hard impacts on solid surface causing a wipe-out of the fuse assembly before the electrical circuits have had time enough to close and actuate the fuse. There currently exists, therefore, the need for an inexpensive reliable contact fuse system that is capable of discriminating between airborne debris and forest canopies and the ground, and that will detonate on any type of ground surface. The present invention is directed toward accomplishing these and other ends.

SUMMARY OF THE INVENTION The present invention provides'a contact fuse assembly adapted for employment on a parachute-dropped weapon that is capable of preventing premature weapon detonation when a tree canopy is encountered, but which permits weapon detonation when substantially any type of ground surface is impacted. The fuse assembly is mounted at the nose of the weapon and consists generally of the following: a base plate which is attached to a shear ring, an open four-legged structure pyramidal in form which is rigidly attached to the base plate, four external" crush switches which are mounted on the outer surface of the base plate between the legs of the pyramid and two internal crush switches mounted on the inner surface of the base plate. A foam pad, which functions in association with the internal switches, is mounted on a bulkhead in the weapon in a position adjacent to the two switches. A cover cone, which protects the external crush switches against accidental activation, completes the assembly and is arranged to be jettisoned after the weapon has been dropped. Two fire signal circuits, each of which contains an internal crush switch and two series connected external crush switches, connect the contact fuse and a weapon detonator. The detonator is fired when either the internal switch or both external switches are closed.

In operation, after the weapon has been dropped and the cover cone jettisoned, if the fuse assembly contacts a tree canopy, the legged structure substantially assures that not more than one of the four external switches will be crushed, thus preventing premature detonation. If the weapon does not contact a tree canopy and the fuse assembly contacts a solid surface, the impact ruptures the shear ring with the base plate being driven inwards crushing the internal switches against the foam pad thus producing ground level weapon detonation. If

the contact fuse, in this case, impacts on mud, water, loose sand and the like, the legged structure penetrates the medium and ground level detonation occurs by the soft material crushing the external switches.

It is a principal object of the invention to provide a new and improved contact fuse system for use in parachute dropped ordinance devices.

It is another object of the invention to provide a fuse system of the type described that is more reliable than currently available fuse systems.

It is another object of the invention to provide a contact fuse for a parachute dropped ordinance device that is capable of discriminating between high forest canopies and forest floors.

It is another object of the invention to provide a contact fuse for a parachute dropped ordinance device that retains electrical circuit completion long enough to fire the detonator 'squibs immediately upon contact with hard ground surface.

It is another object of the invention to provide a contact fuse for a parachute dropped ordinance device that will not permit premature detonation due to rain or aerial debris while the device is being carried by an aircraft.

These, together with other objects, features, and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the illustrative embodiment in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view (cover cone removed) of a contact fuse embodying the principles of the inven tion;

FIG. 2 is a front view (cover cone removed) of the contact fuse of FIG. 1;

FIG. 3 is a section view of FIG. 2 taken at 33; and

FIG. 4 is a schematic view of the electrical fuse detonation circuits of the device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1, 2, and 3 there is illustrated thereby one presently preferred embodiment of the invention. A face plate 9 is affixed to the housing of ordinance device 5 by means of shear joint member 8. Shear joint member 8 is designed to break away from the ordinance device housing at some preselected impact force. External crush switches 12 are surface mounted on face plate 9 as shown. The crush switches used in the present invention can be any appropriate switch of this type currently in use (such as those disclosed in U. S. Pat. Nos. 2,783,320 and 3,458,673). The present illustration of the invention employs two series connected crush switches 12 in each of two redundant circuits. In principle of course a single circuit or multiple circuit can be used and adjacent or diagonal pairs of switches will be effective to carry out the object of the invention. Each external crush switch 12 is provided with a protective grid 13 to prevent circuit closure by aerial debis. An open frame cruciform structure 6 is also mounted on face plate 9 to ward off branches and the like that may prematurely detonate the device. A jettisonable cover cone 15 is provided to further protect the crush switches 12 during carry of the ordinance device by an aircraft. The cover jettisoning apparatus comprises a jettison restraining rod 16 having a flange 17 on one end and a hollow sleeve member 18 threaded onto the other. Spring member 7 is compressed between flange l7 and the collar on cruciform structure '6 and thus maintains a constant jettisoning force.

Sleeve member 18 is provided with holes 20 into which balls 19 are inserted. Balls 20 hold restraining rod 16 in position as they are forced against face plate 9 by the jettison force of spring 7. Rod 21 is inserted into sleeve member 18 and keeps balls 19 in position. A lanyard 23 is connected to the weapons parachute and to rod 21 through tube 22. When the weapon is dropped from an aircraft the parachute pulls on lanyard 23 which retracts rod 21 beyond balls 19 to allow them to fall into sleeve 18. This releases spring 7 and forces nose cover 15, spring 7 and restraining rod 16 out of the way of cruciform structure 6. A rigid fixed bulkhead is provided within the ordinance device housing as shown upon which is affixed a foam rubber pad 11. Interior crush switches 14 are mounted on the inside of face plate 9 and in contact with foam pad 11. It is a feature of the invention that the controlled rupture of shear joint member 8 and the cushioning effect of foam pad 11 prevent a fuse wipe-out when violent impact on a hard ground surface occurs.

FIG. 4 illustrates two identical circuits, which comprise typical circuit redundancy normally employed in weapon systems. On either channel, a fire signal will be conducted by the closing of two external elements or the single internal element. The external elements of each fuse circuitare located on opposite positions on the face of the crush switch assembly. This was done to reduce the probability of both series connected elements being closed when the fuse strikes a glancing blow on a tree branch.

In operation the internal crush elements of the fuse close during nose crush-up as the weapon impacts rock, concrete, or other very hard surfaces. The external elements are intended to close on firm soils, mud or water, by direct particle impingement.

The fuse assembly is constructed to maintain a predetermined failure point around the shear joint mounting surface. When impacting soft to mid-range targets, the fuse structure remains intact as it is carried into the target. On very hard surfaces, where it is possible that the entire assembly might be wiped off before the required electrical signal is conducted, the shear joint lets the conical nose cover 15. Release of this cover can be ac-.

complished by a ball release pin tied to an externally routed lanyard attached to the main parachute. As the parachute fills, the deceleration forces cause the nose cover to separate.

While the invention has been described in one presently preferred embodiment, it is understood that the words which have been used are words of description rather than words of limitation and that changes within the purview of the appended claims may be made without departing from the scope and spirit of the invention in its broader aspects.

What is claimed is:

l. A fuse for a parachute dropped ordinance device comprising aface plate affixed to the nose of said ordinance device, first and second series connected crush switches, said crush switches being mounted on the outer surface of said face plate and electrically connected to actuate an ordinance device firing circuit upon closure of both switches, an open frame switch protecting structure mounted on the outer surface of said face plate, a shear joint connecting said face plate to said ordinance device, said shear joint having rupture characteristics consistent with a selected impact force, a bulkhead member fixedly attached within said ordinance device in close proximity to said face plate, a foam pad member affixed to said bulkhead member adjacent to said face plate and a third crush switch connected to the inner surface of said face plate in contacting relationship with said foam pad, said third crush switch being electrically connected to actuate an ordinance device firing circuit upon closure thereof.

2. A fuse fora parachute dropped ordinance device as defined in claim 1 including a jettisonable cover cone member disposed over said open frame switch protecting member. 

1. A fuse for a parachute dropped ordinance device comprising a face plate affixed to the nose of said ordinance device, first and second series connected crush switches, said crush switches being mounted on the outer surface of said face plate and electrically connected to actuate an ordinance device firing circuit upon closure of both switches, an open frame switch protecting structure mounted on the outer surface of said face plate, a shear joint connecting said face plate to said ordinance device, said shear joint having rupture characteristics consistent with a Selected impact force, a bulkhead member fixedly attached within said ordinance device in close proximity to said face plate, a foam pad member affixed to said bulkhead member adjacent to said face plate and a third crush switch connected to the inner surface of said face plate in contacting relationship with said foam pad, said third crush switch being electrically connected to actuate an ordinance device firing circuit upon closure thereof.
 2. A fuse for a parachute dropped ordinance device as defined in claim 1 including a jettisonable cover cone member disposed over said open frame switch protecting member. 